An ideal visibility algorithm should a) quickly reject most of the hidden geometry in a model and b) exploit the spatial and perhaps temporal coherence of the images being generated. Ray casting with spatial subdivision does well on criterion (a), but poorly on criterion (b). Traditional Z-buffer scan conversion does well on criterion (b), but poorly on criterion (a). Here we present a hierarchical Z-buffer scan-conversion algorithm that does well on both criteria. The method uses two hierarchical data structures, an object-space octree and an image-space Z pyramid, to accelerate scan conversion. The two hierarchical data structures make it possible to reject hidden geometry very rapidly while rendering visible geometry with the speed of scan conversion. For animation, the algorithm is also able to exploit temporal coherence. The method is well suited to models with high depth complexity, achieving orders of magnitude acceleration in some cases compared to ordinary Z-buffer scan conversion.

This thesis presents a volumetric representation for the global illumination within a space based on the radiometric quantity irradiance. We call this representation the irradiance volume. Although irradiance is traditionally computed only for surfaces, its de nition can be naturally extended to all points and directions in space. The irradiance volume supports the reconstruction of believable approximations to the illumination in situations that overwhelm traditional global illumination algorithms. Atheoretical basis for the irradiance volume is discussed and the methods and issues involved with building the volume are described. The irradiance volume method is tested within several situations in which the use of traditional global illumination methods is impractical, and is shown to provide good performance.

f i In this paper we present a method for speeding the process of volume rendering a sequence o mages. Speedup is based on exploiting coherency between consecutive images to shorten the n path rays take through the volume. This is achieved by providing each ray with information eeded to leap over the empty space and commence volume traversal at the vicinity of mean- - b ingful data. The algorithm starts by projecting the volume into a C-buffer (Coordinates uffer) which stores, at each pixel location, the object-space coordinates of the first non-empty s t voxel visible from that pixel. For each change in the viewing parameters, the C-buffer i ransformed accordingly. In the case of rotation the transformed C-buffer goes through a pro- - b cess of eliminating coordinates that possibly became hidden. The remaining values in the C uffer serve as an estimate of the point where the new rays should start their volume traverc sal. This space-leaping method can be combined with existing accele...

this paper, we present a system that exploits object-space, rayspace, image-space and temporal coherence to accelerate ray tracing. Our system uses per-surface interpolants to approximate radiance, while conservatively bounding error. The techniques we introduce in this paper should enhance both interactive and batch ray tracers.

Producing high quality animations featuring rich object appearance and compelling lighting effects is very time consuming using traditional frame-by-frame rendering systems. In this paper we present a rendering architecture for computing multiple frames at once by exploiting the coherencebetween image samples in the temporal domain.

Ray tracing, which computes radiance, is traditionally regarded as an off-line rendering algorithm that is too slow for interactive use. In this paper, we present an interactive system that uses 4D interpolants to approximate radiance, while providing guaranteed error bounds. Our system exploits the object-space, ray-space, image-space and temporal coherence in radiance to accelerate ray tracing. Our system explicitly decouples the two operations of the ray tracer --- shading computation and visibility determination at each pixel, which we call pixel assignment. Rendering is accelerated by approximating the shading computation while guaranteeing correct pixel assignment. Without any pre-processing, the system lazily collects 4D radiance samples, which are quadrilinearly interpolated to approximate radiance. An error predicate conservatively guarantees that the relative error introduced by interpolation is bound by a user-specified ffl. The user can change this parameter to trade off pe...

Coherence denotes similarities between items or entities. It describes the extent to which these items or entities are locally constant. An introduction to coherence and a survey of various types of coherence, that are used in computer graphics, are given. Techniques and data structures for exploiting coherence in computer graphics are described. Incremental techniques, bounding volume schemes, subdivision techniques and several geometric data structures are discussed in more detail. Applications of coherence principles to computer graphics are treated and a survey of previous research is done. INTRODUCTION General remarks The widespread application of coherence principles allows only a vague definition of coherence. Without giving a formal definition coherence denotes, in the context of this paper, similarities between items or entities. It describes the extent to which these items or entities are locally constant. In many situations properties do not change drastically but rather in ...

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Rendering animations requires data structures which allow for an easy handling of the movements and changes in the scene. For a sophisticated renderer, it is very important to access the information describing the motion of the objects, because such knowledge can be used to reduce the render time. We describe an animation model based on an annotated graph, on definitions of dimensions and on implementations of functions. The data structure with its simple interfaces provides an easy to use instrument to produce computer animations. On the one hand, the model is almost independent from a static modeler and a final renderer, but on the other hand, it can be adapted easily to the needs of a specific project. In the current implementation an artist needs to work closely together with a programmer. 1 Introduction Computer animation lives from motion [25]. Primarily, objects in a scene are moving around, but the actions are not restricted to geometrical changes. Almost all parameters such a...

We present a method to reduce the time needed to render a sequence of ray traced images. We exploit the temporal and spatial coherence between consecutive frames. The algorithm does not only inspect the image plane in order to find regions with minor changes